1. Field of the Invention
The present invention relates to a semiconductor device comprising an electrically-rewritable nonvolatile memory cell.
2. Description of the Related Art
A nonvolatile semiconductor memory is exemplified as one of semiconductor memory devices. In recent years, there has been a growing demand for the nonvolatile semiconductor memory used as a data storage device. A NAND-type flash memory is known as a typical electrically-rewritable nonvolatile semiconductor memory using floating gate electrodes.
The NAND-type flash memory is advantageous in downsizing, and thus, increasing its memory density is underway (Jpn. Pat. Appln. KOKAI Publication No. 2005-26590). Currently, dimensions of the memory cell and adjacent memory cells distance have reached 100 nm or less.
A shape of the floating gate electrode gradually becomes vertically long with a dimension decrease in the lateral direction, because coupling ratio of the memory cell should be maintained at a desired value. Therefore, process for forming memory cell shape is getting difficult, and thereby variation of operation characteristics easily arises. Further, parasitic capacitance of the adjacent memory cells increases. Above-mentioned the variation of operation characteristics and the increasing of parasitic capacitance cause memory malfunction.